There are many things that can be done to coax a stubborn CPU into
working. I'll try to mention as many as I can here. Above all, don't
give up until you have exhausted all of your options. Some of the things
you can try are free or low cost, while others may require replacing some
expensive components. Whenever possible, try to eliminate the cheaper
options first. Then, if you suspect you may need to buy a new DIMM or
video card, try to borrow one from a friend first or try your CPU in
another, successfully overclocked system. Remember, it might not be the
CPU at all, but something else in your system that's giving you problems.
Heat
As mentioned in the section on cooling, heat build-up is one of the most
common problems. It manifests itself usually after several minutes to an
hour after start up, especially when running CPU intensive applications.
If you system won't POST (Power On Self-Test), heat is probably not one
of your problems. 1. Try leaving the case open with a table fan blowing
into the case. If the system stays up longer or seems more stable with
the table fan and open case, try some of the cooling methods mentioned
above.
2. Check the temperature of the CPU (front and back sides) and your
video card by gently placing your finger on the heatsink. Be gentle and
only touch the heatsink while your system is running. If it's too hot to
leave your finger in place, you definitely have a heat problem.
3. If the heatsink is applied with thermal tape, try removing it (be
sure to get all of the tape off) and using some thermal grease and/or a
better HS and fan. [If you have a retail Celeron that came with an Intel
fan, I'd save this for last since many, many people have used this fan
without problems. Lately though, I have seen cases reported where
changing the HS/fan did help a retail C300A. It may be that the thermal
tape does not provide enough heat transfer to the heatsink. You could
try just replacing the thermal tape with good old thermal grease and
reinstalling the same Intel HS/fan setup.]
Burn-in
There have been many reports of what is being called "burn-in effect".
After running the CPU at an elevated voltage or even at the normal
voltage while "exercising" the CPU (cycling CPU intensive applications),
the processor somehow becomes more likely to run at the desired speed.
The time required varies and it doesn't always work, but it's worth a
try. If it doesn't run at 100 mHz bus, try 75 mHz or 83 mHz for a few
days. Leave the computer on for several days straight. Give it a
workout, then try it again at 100 mHz. [I have found some documentation
(see web links below) on this effect in respect to audio components. The
author suggested that it may have something to do with dopant
stabilization and the dielectric properties fully forming in the tiny,
in-circuit semi-conductor junctions, capacitors and other components.]
Voltage
Sometimes a little extra voltage is all that's required to encourage your
recalcitrant CPU to straighten up and fly right. You can adjust the
voltage quite easily with the BH6 SoftMenu. It's a little harder with
the P2B but you can still do it. With the BH6 you can increase the
voltage in small increments. Put your system through its paces after
each step. If it still crashes, bump the voltage a little more. You can
fry your CPU by increasing the voltage too much. Use some caution and
common sense here. If voltage is your stumbling block, 2.2 volts
usually does the trick, though some have required as much as 2.3 or more.
The BH6 BIOS will not let you set the voltage higher than 2.3 volts
without a special procedure (found on Andy Drake's site). All Slot 1
motherboards read the required CPU voltage through contacts on the SEPP
(CPU board). By selectively blocking certain contacts, you can "tell"
the P2B (or any motherboard) to raise the CPU voltage. Teflon tape is
one of the best materials to use, however, some people have used nail
polish (dry 24 hours before inserting the CPU) or other non-conducting
varnish. You can even cut the trace, but this technique, while
effective, is difficult to reverse (you need to re-solder over the cut).
This procedure is fraught with pitfalls and, if done incorrectly, can
jolt your CPU with 2.6 volts or more. Since I can't include pictures
with this text document, I recommend examining a web site that
illustrates and details this procedure, if possible (see the list of web
resources at the end of this FAQ). Your choices are quite limited with
this method, but if you have a P2B or other motherboard, it may be your
only option. Notwithstanding those words of caution, here is the list of
pins to cover to get the specified voltages.
Cover up these pins to attain:
2.2v-- A121,A119,B119 (if A119 breaks through, you get 2.6!)
2.4v-- A121,A120,B119 (if A120 breaks through, you get 2.6!)
2.6v-- A121,B119 (not recommended)
2.8v-- A121,A119,A120 (don't even try it)
Heat production increases when you increase voltage, so don't forget
about needing more than ordinary cooling if you need to raise the
voltage. One note of encouragement, there have been many reports of
users being able to revert back to the normal 2.0 volts after a few days
and still maintaining stability (see the section on "burn-in" above).
Drivers and Peripherals
Try different versions of drivers. Try new video drivers, try old video
drivers, try Direct X 5.0 and 6.0. Remove all your cards except the
video card. Disconnect the harddrive and boot from a floppy. If you
have two DIMMS, try with each one individually. Borrow better, or at
least different RAM. Borrow or use an old video card. Overclocking
pushes your whole system to the edge. There is no predicting what device
may be extra sensitive to slight timing errors, data errors or excess
heat. Many of the new video cards, especially the AGP cards run very,
very hot. Be sure that video chip overheating is not what is keeping you
from your desired speed. [My G200 AGP card has hit 145 F when I forgot
to turn on my extra fans. You can mount an old 486 fan on its heatsink
for added insurance.] If you find a card, harddrive or device that's
keeping you from running at 100 mHz, you'll need to replace it.
BIOS
Try getting it to run after disabling the L2 cache in the C300A (L2
should be disabled anyway for the C266 and C300 which have no L2 cache).
Set memory delay settings to higher values. Be sure the AGP setting
(Abit motherboards only) is at 2/3. Set harddrive mode to PIO 4 or 3.
[This is an area I hope to receive comments on from other experienced
Celeron users. How about it?]
-------------------------------------------------------------------------
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Will it damage my CPU or other components?
There are a number of things that could happen to your system through
overclocking but, with a little common sense, you can remove most of the
risk. Heat is the primary concern. The CPU is the system component that
is most likely to suffer from excess heat. Higher clock speeds and/or
higher voltage create more heat. Extreme heat can literally fry the CPU.
Keeping the voltage as close as possible to the default of 2.0 volts and
using a quality heatsink and fan will keep the CPU temperature within
reasonable limits.
Long term effects of higher current produced by faster clock speeds can
have more subtle effects. A process called electro-migration can slowly
erode the microscopic circuits inside the CPU--causing the traces to
spread and the semi-conductor junctions to break down--until the CPU
eventually fails. This is a very slow process and it takes years. A
modern CPU has a design life of 10 to 15 years. While the life of your
overclocked CPU may be somewhat shortened, do you really expect to be
using your current 300 mHz processor, even overclocked to 450 mHz, in
even as little as 5 years? By then we'll all be overclocking 1000 mHz
(giga-Hz) CPU's.
Since BX motherboards like the BH6 and P2B are designed for a 100 mHz bus
speed, you are not likely to hurt the mainboard with speeds up to 100
mHz. The other components, however, can be negatively affected by bus
speeds other than the standard speeds of 66 or 100 mHz. At all other
speeds the PCI and AGP clocks are higher than normal (see the table
below). Besides the obvious effects of increased heat generation, some
peripheral devices are especially sensitive to timing problems when the
PCI bus is over clocked. Some harddrives will trash your data if the PCI
bus is clocked too high .
FSB PCI FSB Ratio AGP FSB Ratio
66 mHz 33 mHz 2 to 1 66 mHz 1 to 1
75 mHz 37.5 mHz 2 to 1 75 mHz 1 to 1
83 mHz 41.5 mHz 2 to 1 83 mHz 1 to 1
100 mHz 33.3 mHz 3 to 1 66 mHz 3 to 2
112 mHz 37.3 mHz 3 to 1 74.6 mHz 3 to 2
124 mHz 41.3 mHz 3 to 1 82.6 mHz 3 to 2
P2B 133 mHz 44.3 mHz 3 to 1 88.6 mHz 3 to 2
BH6 133 mHz 33 mHz 4 to 1 88.6 mHz 3 to 2
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Where can I learn more?
There is an almost inexhaustible supply of information available on the
Internet. Web pages are an invaluable source of additional FAQ's,
reviews and hardware specifics. Any of several Newsgroups and Forums
can provide feedback and answers to specific questions. Below I have
categorized some of the more popular and informative resources that deal
with overclocking. This FAQ is only meant to be an introduction to your
overclocking experience. If you still have problems overclocking after
following this FAQ, you may find additional suggestions and ideas at many
of the following sites.
Newsgroups
------------------
alt.comp.hardware.overclocking
alt.comp.periphs.mainboard.asus
alt.comp.periphs.mainboard.abit
comp.sys.intel
intel.microprocessors.celeron
...
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